Paramecium have been collected from four areas; metropolitan Chicago, rural midwest, and two areas of known metal pollution, one in California and the other in Sudbury, Ontario. Bioassays have revealed large phenotypic differences in copper tolerance among stocks of Paramecium primaurelia and P. triaurelia. No appreciable variability has been observed among stocks of a species from a single location. Among P. primaurelia stocks seven locations had stocks with a median tolerance limit (48 hr), MTL, of 4.7 micrograms copper (II), one location had stocks with an MTL of 13 micrograms copper, and six locations yielded stocks with an MTL of 23 micrograms copper. Among P. triaurelia stock three locations had an MTL of only 3.0 micrograms copper, while four locations yielded stocks with an MTL of 30 micrograms copper. The proposed project will use these stocks and those of P. biaurelia to assess the extent of phenotypic variability in tolerance to the following metals: cadmium, chromium, cobalt, manganese, mercury, nickel and zinc. Genetic analysis of phenotypic differences in metal tolerance within species will be performed. The analysis will focus on: 1. correlations of tolerance with habitat as evidence of adaptation, 2. the dynamics of adaptation as shown by the number of loci with tolerant alleles and their geographical distribution, 3. the metal specificity of metal tolerant genes.